The present invention relates generally to thin film magnetic transducers and, more particularly, to magnetic transducers having a magnetoresistive read transducer utilizing ferromagnetic/antiferromagnetic exchange-coupled bias.
The use of magnetoresistive (MR) sensors to sense magnetically recorded data is well-known in the art. It is also well-known that both longitudinal and transverse bias fields must be provided in the MR sensing element to eliminate Barkhausen noise and to maintain the sensor in its most linear operating range. Commonly assigned U.S. Pat. Nos. 4,024,489; 3,840,898 and 4,103,415 disclose MR sensors which utilize various biasing schemes including the use of both hard and/or soft magnetic materials to provide the longitudinal and transverse bias magnetic fields required by the MR sensing element.
It has become increasingly difficult to fabricate MR read transducers in the small physical size required to read data recorded on ever decreasing track widths at ever increasing linear recording density. One solution proposed to meet these requirements is described in commonly assigned U.S. Pat. No. 4,663,685 in which a transverse bias field is produced in only a central active region of the MR sensor element and a longitudinal bias field is produced in the inactive end regions by means of exchange coupling between the portions of the ferromagnetic MR element which extends into the end regions and layers of antiferromagnetic material which extend only over the end regions of the MR element. U.S. Pat. No. 4,639,806 discloses an MR sensor which provides a longitudinal bias field produced by ferromagnetic exchange coupling between the MR layer and hard magnetic layers in the sensor end regions only. Commonly assigned U.S. Pat. No. 5,079,035 discloses an MR sensor in which the ferromagnetic MR element extends over only the central active region of the sensor. A layer of hard magnetic material is provided in each of the sensor end regions which forms an abutting junction with the ends of the MR element to provide a longitudinal magnetic bias field in the sensor. The central active region includes the MR element, a non-magnetic spacer layer and an adjacent soft magnetic layer which provides a transverse magnetic bias field for the sensor.
The MR sensor design described in U.S. Pat. No. 5,079,035 has been shown to meet present requirements and provides numerous advantages including, data track definition by a single photolithography process step, controllable and reproducible etch step of the sensor active region trilayer etch process, easily adjustable longitudinal bias field, and substantially no side reading. The contiguous or abutting junction hard bias design suffers from a substantial disadvantage at relatively narrow data track widths where the length of the MR sensor active region can be comparable to or even small compared to the length of the junction which can cause the magnetic properties in the junction region to no longer be predictable or well-defined. As a result, under transverse field excitation, hysteresis can be introduced into the sensor's response. However, at large data track widths where the length of the MR sensor active region is large compared to the length of the junction region, any resulting hysteresis is typically not detectable. In addition, the magnetization of a cobalt (Co) alloy hard ferromagnetic material, when grown on different substrates, such as the trilayer active region of the sensor at the overlayping junction region, causes a majority of the Co c-axes to be oriented perpendicular to the film plane. Thus after initialization with a longitudinal magnetic field, such a hard ferromagnetic layer will have substantially no remnant magnetization and the magnitude of the longitudinal bias field thus produced can be insufficient to insure a single domain state in the sensor.